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Low water PSI on oil fired hot water furnace

Is it normal for the water pressure gauge to only read 0-5 PSI? When the furnace turns off at ~ 180F, the water pressure is about 4-5PSI. There's considerable amount of water deposits coming out from the expansion tank safety valve and a lot of gurgling in the baseboards. Based on my experience when I had a hot water furnace the gauge should always read 10-15PSI. Not looking to DIY, just determining if this is normal and, if not, how long I should wait to call a service tech. Thanks in advance.

You really do have multible problems and do have a dangerous situation.You need service right away.
While they are there,residential low water cut off is fairly cheap and easy to install.If I were you I would also have a spirovent installed These are a couple of things that could be reused on a new boilwer if that is the way you go and well worth the cost.

I advised my father in law to call a service rep and sure enough the relief on the expansion tank was bad along with the backflow valve. Unit was low on water but after repair pressure ranges from 15-20PSI on/off. I knew something didn't sound right that morning....